I've been doing some research of my own and while i have more to test, here's what i came up with. For most of these tests i used the Telia amss.mbn (since it has the latest build date), but they all share the same default settings for this.
HSPA (= HSDPA+HSUPA):
HSDPA is covered in 3GPP release 5, while HSUPA is part of release 6.
While references to HSUPA and HSPA in amss.mbn can be found, in all gen2 versions i have seen, only release 5 is exposed by the Radio Resource Control (RRC). With some specific settings in the non-volatile memory (where IMEI and other things are stored), it was possible to force this to 6.
While the phone worked normally, every time HSPA would be activated, it would reboot and the logs don't really show what goes wrong (it stops at different spots with different tries).
For example, from the radio log (adb logcat -b radio):
E/QCRIL ( 191): UMTS System: srv domain 3 , srv capability 3, egprs supp 0
E/QCRIL ( 191): HSPA System
E/QCRIL ( 191): Registration State: Registered (Home network), RadioTech: HSPA, LAC: xxxx, CID: xxxxxxxx, BSID: (null), BSLat: (null), BSLong: (null)
E/QCRIL ( 191): CCS: (null), SID: (null), NID: (null), RoamStatus: (null), PRL: (null), DefRoamStatus: (null), RejReason: 0
D/GSM ( 309): radio tech is 11
(radio tech 11 = HSPA, 9 = HSDPA)
This doesn't necessarily mean it will reboot for anyone, but with the currently available firmware, it is always put back to release 5 when you start up your phone, so HSUPA shouldn't work. (If you think it does, the radio log should show it.)
The current amss.mbn's don't enable 850 for either 2G or 3G. From code, it seems only the Chinese amss.mbn unlocks both 2G and 3G 850, but i haven't been able to get that one to work.
Enabling 2G 850 seems fairly easy (my phone is running with it, but i have no way to test it atm!); from a log:
rr_general.c 01922 UE supports EGSM900 and PGSM900
rr_general.c 01941 UE supports DCS1800
rr_general.c 01950 UE supports PCS1900
rr_general.c 01958 UE supports GSM850 [this line is new]
No luck on 3G 850 yet.